Difference between Incremental & Differential backups

Incremental Backup: Any changes since the last backup.

Differential Backup: Any changes since the last FULL backup.

Incremental will be roughly the same size every night. Differential will get bigger towards the end of the week.

When it comes to doing a restore, with Incremental you will need the Full, plus each incremental since the full (i.e. on  a Thursday you will need Friday full, plus Mon, Tue and Wed night tapes - assuming no sat/sun backup)

When restoring with Differential you will need the last full, plus the latest differential.  

Therefore differentials are quicker for doing a full restore, but need more space and time to backup, particularly towards the end of the week.

 e.g.

Backup Type	Data backed up	Backup Time	Restore Time	Storage Space
Full Backup	All Data	Slowest	Fast	High
Incremental backup	Only new/modified files folder	Fast	Moderate	Lowest
Differential Backup	All data since last full backup	Moderate	Fast	Moderate